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Oct. 4, 2011 -- Eighteen people now are confirmed dead in the ongoing listeria outbreak from contaminated cantaloupes.

The CDC confirms that 100 people in 20 states have been infected with one of the four outbreak strains of Listeria monocytogenes.

Listeria frequently causes miscarriage, stillbirth, or preterm birth when it infects a pregnant woman. Two pregnant women have been infected in the current outbreak. The CDC reports that "the outcome of each pregnancy is being monitored."

The contaminated cantaloupes came from Jensen Farms in Holly, Colo. All of these cantaloupes were recalled on Sept. 14. All were shipped by Sept. 10. Since cantaloupes have a shelf life of about two weeks, few if any of the melons are still being eaten.

But listeria can take up to two months to cause serious illness -- and it takes longer for these illnesses to be reported. The CDC notes that illnesses beginning after Sept. 7 may not yet be reported. That means the case count, and death toll, is likely to rise even further.

There have been five deaths in Colorado, two in Kansas, one in Maryland, one in Missouri, one in Nebraska, five in New Mexico, one in Oklahoma, and two in Texas.

The states reporting cases are:

Alabama (1 case)

Arkansas (1)

California (1)

Colorado (30)

Idaho (1)

Illinois (1)

Indiana (2)

Kansas (7)

Maryland (1)

Missouri (3)

Montana (1)

Nebraska (6)

New Mexico (13)

North Dakota (1)

Oklahoma (11)

Texas (14)

Virginia (1)

West Virginia (1)

Wisconsin (2)

Wyoming (2)

Nearly all people infected in the outbreak have been hospitalized. Most illnesses are in people over age 60. The ages of those sickened in the outbreak range from 35 to 96 with a median age of 79.

Cantaloupes that are known not to come from Jensen Farms are safe to eat.

According to the CDC, people who have eaten listeria-contaminated cantaloupes (or other foods) do not need to seek medical attention unless they have symptoms.

Listeriosis Symptoms

The disease caused by listeria bacteria is called listeriosis. Although listeriosis is a food-borne illness, when you have symptoms of the disease it usually means the bacteria have escaped the digestive tract and are spreading throughout the body. Listeriosis often results in fatal meningitis or encephalitis.

Listeriosis usually begins with diarrhea or other intestinal symptoms. Patients soon develop fever and muscle aches. What happens next depends on a person's risk factors:

While pregnant women usually get a mild flu-like illness, listeria infection can cause miscarriage, stillbirth, premature delivery, or fatal infection of the newborn.

Symptoms may occur as soon as three days or as long as two months after infection. The typical incubation period is thought to be one to three weeks.

Foods typically linked to listeriosis are deli meats, hot dogs, and soft cheeses made with unpasteurized milk. Produce is less often linked to outbreaks, although listeria is found in soil and water. Listeria is killed by cooking, but it can grow and multiply in refrigerators.

How to Avoid Listeria

The CDC has issued this advice:

People at high risk for listeriosis, including older adults, people with weakened immune systems, and pregnant women, should not eat cantaloupes marketed as coming from the Rocky Ford region of Colorado.

People who have cantaloupes in their homes can check the label or inquire at the store where they purchased it to determine if the fruit was marketed as coming from the Rocky Ford region of Colorado.

Listeriosis primarily affects older adults, people with weakened immune systems, pregnant women, and newborns. People who think they might have become ill from eating possibly contaminated cantaloupes should consult their doctor immediately.

Cantaloupes marketed as coming from the Rocky Ford region should be disposed of in a closed plastic bag placed in a sealed trash can. This will prevent people or animals from eating them.

As other foods besides cantaloupes can carry listeria, the CDC recommends these general steps to avoid listeriosis:

Rinse raw produce, such as fruits and vegetables, thoroughly under running tap water before eating. Dry the produce with a clean cloth or paper towel before cutting them up.

Thoroughly cook raw meat and poultry.

Heat hot dogs, deli meats, and cold cuts until they are steaming hot just before serving.

Do not drink raw (unpasteurized) milk and do not eat fresh soft cheeses that have unpasteurized milk in them, especially Mexican-style cheeses like queso fresco.

Be sure that your refrigerator is at or below 40 degrees F and your freezer is at or below 0 degrees F by using a refrigerator thermometer.